Studies will be made of the chloroplast phosphorylation system. The action of sulfate on energized chloroplasts will be explored further with attention to blocking effects on further sulfate inhibition, of components of the medium modified during exposure to light. A spin label material is covalently attached to the chloroplast coupling factor (CF1) during incubation in the light; its spin is immobilized until after trypsin activation of the ATPase and studies will be made to find similar indications of light and electron-transport-induced changes in environment of the probe. A possible specific site for damage to a limited number of amino acid residues by low concentrations of permanganate, acting in a light-and ADP- dependent reaction, will be sought. This includes tracing down those cysteine molecules oxidized to cysteic acid in the CF1 exposed to permanganate only after preliminary blocking with NEM in the dark. Attempts will be made to solubilize the subunits of CF1 using a reversible anhydride modifier of amino groups (such as dimethylmaleic acid). These studies are aimed at the possibility of recombining subunits to form an active enzyme again. Other modifiers of amino groups (imido esters, TNBS) are being tested for possible differential binding and differential physiological effects depending on the state of CF1 during exposure.